The invention relates to a metallic flat gasket which is suitable, in particular, as a cylinder head gasket for utility vehicles. In cylinder head gaskets, the sealing of the combustion chamber openings, in exhaust manifold gaskets of the combustion gas openings, is particularly important. In order to ensure a reliable seal in this region, it is therefore necessary, in particular in applications such as are conventionally encountered in commercial vehicle diesel engines with or without cylinder liners, to concentrate the screwing force on the combustion chamber with which the cylinder head and motor block are joined together. In order to achieve this, it is conventional in cylinder head gaskets for internal combustion engines having a small or no liner projection to provide a so-called protrusion at the edge of the combustion chamber. This means that, in the region around the combustion chamber openings, the overall thickness of the gasket layers of the cylinder head gasket, including a small liner projection or setoff which may be present, is greater than the overall thickness of the gasket layers in regions of the gasket that are more remote from the combustion chamber openings, i.e., the so-called “hinterland”.
A protrusion of this type at the edge of the combustion chamber is frequently achieved using what is known as a stopper. These stoppers are usually solid annular inlays extending directly along the edge of the combustion chamber. The stoppers are generally of a height such that they, in combination with the thickness of the gasket layers present in the region around the combustion chamber opening, completely fill the sealing gap between the motor block and cylinder head in the region around the combustion chamber opening. As an alternative to inserting a separate ring, the stopper can also be produced by bending an edge portion of the gasket layer at the combustion chamber opening. Stoppers of this type have no elastic properties. In order to achieve reliable sealing of the combustion chamber openings, stoppers are therefore conventionally used in combination with an elastic sealing element, generally a bead, which conventionally extends, viewed from the combustion chamber opening, radially outside the stopper. Generally, the stopper serves at the same time also as a support element for the bead and prevents complete flattening thereof during operation of the gasket. The attachment of a stopper radially behind the bead, as an alternative or in addition to the stopper at the edge of the combustion chamber, is also known in the art. Furthermore, there are solutions in which an elastic bead is combined with a separate rigid element in such a way that both are at a comparable radial distance from the edge of the combustion chamber.
The construction of the stopper-bead gaskets is comparatively complex. In addition, it is often necessary, in order to obtain reliable sealing of the combustion chamber openings, to topographically configure the region of the cylinder head gasket around the combustion chamber openings. Without such a topographical configuration, the clamping pressure/force exerted by the fastening means in the circumferential direction around the combustion chamber openings would often be non-uniform. A plurality of screws are conventionally distributed around the combustion chamber opening for fastening the cylinder head to the motor block. In the built-in state, the distance between the cylinder head and cylinder block is usually greater in the region between the screws than on the screws themselves. As a result, the size of the sealing gap to be filled by the cylinder head gasket which is arranged between the motor block and cylinder head gasket increases. This sealing gap variance is allowed for by an appropriate topography of the cylinder head gasket around the combustion chamber openings. It is for example known to configure the height of the stopper in the circumferential direction around the combustion chamber opening in accordance with the size of the sealing gap. The manufacture of such a topography in solid stoppers is however often complex and difficult.
An alternative solution for the sealing of combustion chamber openings in cylinder head gaskets for utility vehicle engines consists in using, instead of a stopper-bead combination, a purely plastic bead at the edge of the combustion chamber. This purely plastic bead, which can also be a multiple bead extending in a plurality of concentric rings around the combustion chamber opening, has, in contrast to the beads of the stopper-bead gaskets, almost no elastic properties. However, this lack of elasticity often leads to unsatisfactory sealing properties around the combustion chamber openings. In order to obtain the required rigidity, the plastic beads are in addition frequently provided with what is known as a hard coating or the bead cavity is filled with a rigidifying material. This complicates and increases the cost of the manufacture of a gasket of this type.
There was therefore a need for a metallic flat gasket and in particular a cylinder head gasket for internal combustion engines that leads, while maintaining a simple construction, to reliable sealing of the through-openings and in particular of the combustion chamber openings in the case of cylinder head gaskets. The object of the invention is accordingly to devise a metallic flat gasket of this type.
This object is achieved by the metallic flat gasket according to claim 1. Preferred embodiments of this flat gasket are described in the sub-claims.